The dba_replace function in PHP 5.2.6 and 4.x allows context-dependent attackers to cause a denial of service (file truncation) via a key with the NULL byte. NOTE: this might only be a vulnerability in limited circumstances in which the attacker can modify or add database entries but does not have permissions to truncate the file.
http://cvs.php.net/viewvc.cgi/php-src/NEWS?r1=1.2027.2.547.2.1313&r2=1.2027.2.547.2.1314&